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Questions and Answers
Which gyrus is involved in auditory processing and receptive language?
Which gyrus is involved in auditory processing and receptive language?
What is the main function of the reticular activating systems (RAS) found in the hypothalamus and brainstem?
What is the main function of the reticular activating systems (RAS) found in the hypothalamus and brainstem?
What is the abbreviation for Auditory Middle Latency Response?
What is the abbreviation for Auditory Middle Latency Response?
What type of stimulus is recommended for neurodiagnostic purposes?
What type of stimulus is recommended for neurodiagnostic purposes?
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What is the recommended duration for a click signal in AMLR testing?
What is the recommended duration for a click signal in AMLR testing?
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Study Notes
Middle Latency Response (MLR)
- First reported by Geisler, Frishkoph, and Rosenblith in 1958
- MLR is a series of waveforms occurring from 10-80 ms after the onset of an auditory stimulus
Components of MLR
- Consists of 2 positive and 2 negative peaks, labelled as Na, Pa, Nb, and Pb
- Normal latency range for each peak:
- Na: 16.25-30.00 ms
- Pa: 30.00-45.00 ms
- Nb: 46.25-56.25 ms
- Pb: 56.25-80 ms
- Wave amplitudes range from 0.25 to 3.0 µV
Generators of MLR
- Multiple generators contributing to the waveform
- Secondary auditory cortex (Wernicke's zone-Brodmann's area 22) receives afferents from the dorsal and medial subnuclei of the medial geniculate nucleus
- Primary auditory cortex lies between the sylvian fissure and superior temporal gyrus
- Auditory cortex (primary/secondary) with possible upper brainstem and thalamic contributions
Peak Generators
- Na: Mostly from sub-cortical regions of the auditory system, specifically MGB of thalamus, thalamocortical region, and portions of the inferior colliculus and Heschl's gyrus
- Pa: Superior temporal gyrus within the auditory cortex
- Nb: Still unclear
- Pb: Auditory cortex, perhaps the posterior region of the planum temporale and even hippocampus
Nomenclature
- Goldstein & Rodman introduced the labels Na, Pa, and Nb in 1967 to describe the MLR components
- Other terminologies include Auditory Middle Response (AMR), Middle Latency Response (MLR), and Middle Latency Auditory Evoked Potentials (MLAEP)
Test Protocols
- Parameters:
- Stimulus: Click or tone-burst signals
- Transducers: ER-3A or insert earphones
- Duration: 0.1 ms for click signals, 2 cycles for tone-burst signals
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Description
Learn about the Middle Latency Response in electrophysiological assessment of the auditory system, including its components and historical background. Submitted by Perpetua Nancy S, M.Sc Audiology.
